The sphinctometer is a solid-state device system for prolonged ambulatory recordings of the lower esophageal sphincter (LES) pressure. The aims of this study were to determine 1) the pressure sensitivity and the latency of sphinctometer responses in vitro, 2) if the sphinctometer can record transient LES relaxations (TLESR) in vivo, and 3) if the currently accepted criteria for TLESR are applicable to sphinctometer recordings. Different segments of the sphinctometer were positioned in a chamber at known pressures to assess the sphinctometer readings as well as the latency of the response. Ten healthy subjects were investigated with the use of a solid-state transducer sphinctometer assembly and a pH probe for 4 h. The LES pressure was analyzed during baseline periods, swallow-induced LES relaxations (SILESR), and LES relaxations associated with acid reflux episodes (pH <4) (presumed TLESRs). Our results showed that sphinctometer readings were linearly related to the chamber pressure and the length of the segment exposed to the pressure; however, the latter was considerably underestimated. We also found that sphinctometer segments of equal length but at different levels showed different pressure readings, the mean response time of sphinctometer was 0.25 s, and sphinctometer output was susceptible to temperature changes of the environment. In humans, only 25 of 45 episodes (64%) and 17 of 22 episodes (77%) were detected by the sphinctometer as being SILESRs and TLESRs, respectively. The pattern of the LES pressure during acid reflux events resembled classical TLESR. We concluded that the sphinctometer is a useful device for determining qualitative changes in LES pressure. However, its major limitations are pressure underestimation, different sensitivity of various segments, pressure drifts, and underscoring of LES relaxations.